Relatively large types of gaskets are used for the inlet manifolds, filter blankets, cylinder head covers, etc. of automobile engines by inserting the gaskets between two members, one of which has a groove for insertion to effect tight sealing therebetween. To meet the recent trend for making the engine weight lighter, the engine members are now made from resins or aluminum, and consequently the rigidity of members becomes lower. Thus, the gaskets of a lower reaction force are now desired. Gaskets in a shape of larger longitudinal cross-section as viewed from the width direction of the gasket (a shape of larger cross-sectional height with respect to the cross-sectional width) have been generally used.
Patent Literature 1: JP-A-2003-269613
Patent Literature 2: JP-A-2002-21635
It is desirable for making gaskets having a lower reaction force to use rubber materials of low hardness, but in the case of inserting such gaskets of relatively large type, in a shape of larger longitudinal cross-section as viewed from the width direction, and made of materials of low hardness, into grooves in engine members having various complicated shapes, the gaskets are easily susceptible to torsion in the insertion working, lowering the working efficiency, or the inserted gaskets undergo partial flexure or elongation, making it hard to conduct uniform insertion, and consequently often causing leakage at the time of compression tight sealing or compression cracking of gaskets.
In this connection, it has been proposed to provide a gasket with a frame to enable automatic insertion, specifically a cover gasket to be inserted between a cover member and a fixing member, provided with a projection protruded from the outer side surface of elastic body of the cover gasket into a thicker shape towards the tip end of the projection, and also provided with a reinforcing rod coming out from the outer side surface of the cover gasket to enclose the projection, or a gasket comprising an insert material with a raised part, and a seal member, as inserted into a gasket insertion position of a cover member with a vertically suspended-down, exertion part, thereby ensuring exertion of a precise surface pressure, enhancing a tight sealing performance and keeping a better shape to enable mechanically automatic fixing.
Patent Literature 3: JP-A-2000-130591
Patent Literature 4: JP-A-2002-243042
In such structures, however, the frame must be molded to meet the desired dimensions of fixing member in advance, and a gasket must be integrally molded to match up with the frame, making the production process complicated. In the case of a gasket in a three-dimensional shape, as shown in FIG. 1 of the following Patent Literature 5, integral molding of the gasket to match up with the frame is a difficult problem.
Patent Literature 5: JP-A-2002-71024
On the other hand, it has been also proposed to embed a rigid core body into a gasket body as an ordinary method for improving the working efficiency of gaskets, more specifically, a gasket made by integration of a core body with an elastic material, where the entire peripheral surface of the core body formed into a frame shape of most thereof is coated with the elastic material. In that case, molding of the core boy in advance is a complicated problem and an exact placement of the core body at a predetermined position of the gasket cross-section, for example, at a center portion, at the time of molding, is also a difficult problem. Furthermore, a gasket provided with a core body of high rigidity, such as metals, resins, etc. has a problem that the gasket itself has a higher reaction force, and also such further problems that a high shearing stress arises at the boundary surface between the rubber material and the core body, causing peeling to take place at the boundary surface therebetween.
Patent Literature 6: JP-A-2001-4031